Nondusting, high temperature dryer

ABSTRACT

Apparatus and method for low dust level drying of material in continuous drying apparatus of the type utilizing a plurality of vertically superimposed, rotating trays to convey the material through the dryer. Billowing of the material, and hence dust formation, is retarded by delivering the material to the dryer, and thereafter transferring it between vertically adjacent trays, through inclined chutes. Upon each revolution of the trays, wiper arms guide the material on each tray over the edge of the tray, while other wiper leveler and leverler arms distribute the material discharged on to each tray from the next higher tray over the surface of the tray. All side and both end walls of the dryer housing are thermally insulated to maintain high drying temperatures, and the skeletal support structure, as well as the trays and end walls of the housing, are constructed to expand or contract laterally in response to temperature changes within the housing, thus allowing uninterrupted operation of the dryer over a wide range of temperatures, including highly elevated temperatures.

United States Patent [1 1 Weisselberg et a1.

[ Dec. 11, 1973 NONDUSTING, HIGH TEMPERATURE DRYER [75] Inventors:Edward B. Weisselberg, Old

Tappan; George M. Worden, Sr., Park Ridge; William F. Lamp, Closter;Alexander M. Lane, Allendale, all of [73] Assignee: Wyssmont Company,lnc., Fort Lee,

[22] Filed: May 5, I972 [21] Appl. No.: 250,621

Related US. Application Data [62] Division of Ser. No. 8,985, Feb. 5,1970, Pat. No.

18,440 5/1908 Norway Primary Examiner-Carroll B. Dority, Jr.

Assistant Examiner-Larry I. Schwartz AttorneyBrumbaugh, Graves, Donohue& Raymond [57] ABSTRACT Apparatus and method for low dust level dryingof material in continuous drying apparatus of the type utilizing aplurality of vertically superimposed, rotating trays to convey thematerial through the dryer. Billowing of the material, and hence dustformation, is retarded by delivering the material to the dryer, andthereafter transferring it between vertically adjacent trays, throughinclined chutes. Upon each revolution of the trays, wiper arms guide thematerial on each tray over the edge of the tray, while other wiperleveler and leverler arms distribute the material discharged on to eachtray from the next higher tray over the surface of the tray. All sideand both end walls of the dryer housing are thermally insulated tomaintain high drying temperatures, and the skeletal support structure,as well as the trays and end walls of the housing, are constructed toexpand or contract laterally in response to temperature changes withinthe housing, thus allowing uninterrupted operation of the dryer over awide range of temperatures, including highly elevated temperatures.

13 Claims, 12 Drawin liigures PATENTEUUEC 1 1 I975 SHEET 3 OF 7 No m2WFNIEIJUER H 1975 3.7771409 sum 0F 7 COOLING AIR PATENTEU DEC 1 1 I975SHEET 8 BF 7 NONDUSTING, HIGH TEMPERATURE DRYER This is a division ofapplication Ser. No. 8,985, now U.S. Pat. No. 3,681,855 filed Feb. 5,1970.

BACKGROUND OF THE INVENTION The present invention relates to continuousrotary tray dryers of the kind having a plurality of verticallysuperimposed trays for conveying the material through the dryer bysuccessively transferring the material from tray to tray, and, moreparticularly, to apparatus and method for processing material in rotarytray dryers while retarding billowing of the material, and hence dustcreation, as it is advanced through the dryer. Additionally, theinvention is directed to continuous dryers of this type in which thedryer housing is fully insulated, and the dry skeletal structure andmaterial carrying surfaces constructed to allow thermally inducedexpansion or contraction thereof, to facilitate uninterrupted operationof the dryer at elevated temperatures.

Continuous rotary tray dryers of the kind referred to are known and, infact, have found .wide acceptance in many industries. Such dryers aremanufactured under the trademark TURBO-Dryer by the Wyssmont Company,Inc., 1470 Bergen Boulevard, Fort Lee, N.J., the assignee of the presentapplication. The Wyssmont dryers generally produce a finished product ofhigh quality and uniformity even where such diverse materials arecrystals, powders, pellets, gels and slurries are processed through thedryers and where both high and low drying rates or material outputs arerequired.

It is desirable in certain applications, however, and in particularwhere finely divided or fragile materials are to be dried, that specialprovisions be made for minimizing billowing or breakage of the materialas it is conveyed through the dryers so as to retard dust formation.High dust levels within a dryer sometimes lead to operationaldifficulties, such as explosion hazards and clogging of the dryer andits associated equipment, which result in reduced drying efficiency andincreased costs. Moreover, by keeping dust levels within the dryer at aminimum, the need for elaborate dust collection and material returnequipment at the exit end of the dryer and, where the drying medium isrecirculated, the need for gas cleaning and process equipment can besignificantly reduced and, i some instances, entirely eliminated.

It is important also that continuous operation of the dryer at elevatedtemperatures be possible without interruption due to warping ordistortion of the dryertrays or supporting framework caused bydifferences in temperature between the interior and exterior of thedryer or by temperature variations within the dryer'itself. Accordingly,apparatus is needed which will allow for thermally induced expansion andcontraction of critical dryer components to the extent necessary topermit operation of the dryer at the desired temperatures.

SUMMARY OF THE INVENTION In accordance with the present invention, dustlevels are minimized in continuous rotary tray dryer apparatus bydelivering the material to an upper tray in the dryer through aninclined chute, and thereafter transferring the material through thedryer from tray to tray by passing it through inclined chutes whichextend between vertically adjacent trays. Upon rotation of the trays,wiper arms associated with each tray guide the material over thelaterally outer edges of the trays and into the upper ends of theinclined chutes, while additional wiper arms and leveler arms associatedwith each tray distribute the material transferred to the tray from thenext highest tray evenly over the surface of the tray. Thus, thetransfer of the material through the dryer is very gentle, in innegligible breakage, minimum formation of fines and minimum adhesion ofthe material to the trays or to the transfer arms and chutes.

As the material advances from tray to tray in the dryer, the lateralposition of the material on the tray is alternated; that is to say, thematerial occupying the laterally outer portion of one tray, upon beingtransferred to the next lowest tray, is directed to and spaced over thelaterally inner portion of the lower tray. Conversely, the portion ofthe material that occupied the laterally inner portion of the highertray is moved to the laterally outer portion of the lower tray. Allsurfaces of the material are thus sought to be uniformly exposed to thedrying medium.

High temperature operation of the dryer is made possible through acombination of insulating the dryer housing against heat loss andconstructing the load bearing skeletal structure and material carryingsurfaces of the dryer to permit lateral expansion and contraction ofthese components in response to temperature variations. Economies ofoperation are thus realized, as heat losses are kept at a low level, asignificant cost factor at high operating temperatures, and operationaldifficulties such as warping or jamming of the rotating trays areavoided. Moreover, greater flexibility of use of the dryer is achievedin that high temperatures can be maintained in theupper portions of thehousing to dry quickly and uniformly the materials delivered to thedryer, while the lower stages of the dryer can be used to cool the driedmaterial prior to its discharge from the dryer. Although large verticaltemperature gradients will exist in such instances, the insulationstructure and thermal expansion and contraction capabilities of thedryer permit continuous, uninterrupted operation of the dryer,withaccurate temperature control at the various drying and coolingstages.

The insulation structure for the dryer housing includes panel units thatextend between the-vertical support columns spaced around the housingperiphery and individual, elongate insulator members positioned adjacentthe exterior side of each support column, thereby tending to maintainthe temperature of the support columns at or near the temperature of themore laterally inward portions of the housing. Insulated wall assembliesare located across both the upper and lower ends of the housing. Theupper wall assembly includes a hot roof and a cold roof, with the hotroof being suspended from the cold roof in a manner to be laterallymovable relative to the cold roof..Aligned openings provided in the hotand cold roofs to admit the various heating elements, drying mediumducts, material inlet assembly, etc., associated with the dryer to theinterior of the housing are oversized to an extent that expansion of thehot roof during operation of the dryer will not be impaired byengagementof the roof edges with the elements extending through theopenings.

Expansion joints are provided at both ends of the vertical columns sothat the columns may be displaced laterally as the housing expands orcontracts during operation. Expansion or contraction of the trays andbottom wall, which preferably are segmented, is provided for bysupporting the inner ends of the tray segments on a floating annularring and by slidably clamping the tray and bottom wall segments toradial support arms and an outer annular ring carried by the radialsupport arms.

Preferably, slightly negative pressure is maintained I within thehousing to provide an inward flow of air at any position on the dryerhousing where leakage of dust or drying medium from the housing might beexpected. Also, at the bearings journaling the lower and upper ends ofthe tray shaft a pressurized flow of air is provided to prevent leakageof dust along the shaft and also to cool the bearings to temperaturessubstantially below those maintained within the dryer.

BRIEF DESCRIPTION OF THE DRAWINGS For a better understanding of theseand other aspects of the invention, as well as the objects andadvantages thereof, reference may be made to the following detaileddescription and to the drawings, in which:

FIG. 1 is a side elevational view of a continuous rotary tray dryerconstructed in accordance with the present invention showing thelocations and orientations of the thermal expansion joints on thevertical support columns of the dryer housing;

FIG. 2 is a plan view taken along the line 2-2 of FIG. 1 and looking inthe direction of the arrows, with parts broken away from clarity ofillustration;

FIGS. 3A and 3B are partial vertical sectional views of the upper andlower ends of the dryer taken along the line 3-3 of P162 and looking inthe direction of the arrows, with parts broken away for clarity;

FIG. 4 is an enlarged detail view of the material inlet chutearrangement of the invention taken along line 44 of FIG. 2 and lookingin the direction of the arrows;

FIG. 5 is a horizontal view taken along the line 5-5 of FIG. 4 andlooking in the direction of the arrows;

FIG. 6 is a horizontal sectional view taken along the line 66 of FIG. 3Band looking in the direction of the arrows, with parts broken away forclarity of illustration;

FIG. 7 is a vertical sectional view taken along the line 77 of FIG. 6and looking in the direction of the arrows, with parts broken away forclarity;

FIG. 8 is an enlarged detail view of the bottom wall and material outletchute arrangement of the invention taken along the line 88 of FIG. 3Band looking in the direction of the arrows;

FIG. 9 is an enlarged vertical sectional view taken along the line 9-9of FIG. 8 and looking in the direction of the arrows;

FIG. 10 is an enlarged vertical sectional view taken along the line l010of FIG. 8 and looking in the direction of the arrows; and

FIG. 11 is an expanded schematic illustration of the circumferentiallocations of the material transfer chutes extending between verticallyadjacent trays and of the paths followed by the material as it advancesthrough the dryer.

DESCRIPTION OF AN EXEMPLARY EMBODIMENT In FIG. 1, a continuous dryerconstructed in accordance with the invention includes a generallyoctagonshaped housing having a skeletal support structure includingload-bearing columns 22 located at the apices of the housing sides, alower support frame 24 for the columns 22 and the drive equipment forthe dryer, and an upper support frame 26 for carrying the dryer heatingelements, intake and exhaust manifolds and associated equipment and fortransmitting the load of this equipment to the support columns 22.

The columns 22 also support a plurality of panel units 28 which,together with an upper wall assembly 30 and a lower wall assembly 32,define an enclosed drying zone within the housing 20. As is more fullydisclosed hereinafter, girth members extend peripherally betweenadjacent columns and with the columns carry the panels 28 and wallassemblies 30 and 32.

A combustion fuel is delivered, as indicated by the arrows in FIGS. 1and 3A, through an intake manifold (not shown) and pipes 34 toadjustable metering devices 36 and chambers 38, where it is mixed withair delivered through pipes 40. The gas-air mixture is then burned ingenerally U-shaped heating elements 42, to raise and maintain thetemperature of the housing interior to the desired magnitude, and isexhausted, together with the combustion products produced in theelements 42, to an exhaust manifold 44 and thereafter to a stack (notshown) in communication with an exhaust duct 46 (see FIG. 1). As clearlyrepresented in FIG. 2, several heating elements 42 are spaced around theinner walls of the housing 20, with a corresponding number of meteringdevices 36 and chambers 38 being provided so that the heat generated byeach element 42 can be individually regulated. The exhaust manifold 44(see FIGS. 1 and 3A) takes the configuration of a partial annulus and isarranged to extend above each of the exhaust legs of the heatingelements 42 to facilitate connection with the elements, as, for example,by means of the ducts 48. If desired, the exhaust duct 46 and theconnector ducts 48 may be covered with insulating material to reduceheat losses and to keep temperaturesat the upper end of the dryer frombecoming too high.

Instead of burning a gas-air mixture within the heating elements 42, ahigh temperature transfer liquid can be circulated through the elements.Also, steam, oil or electricity can be used as the heat source ratherthan a combustible gas.

A drying medium, such as air, inert gas or superheated steam, isadmitted into the housing 20 through intake ports (not shown) and iscirculated over the heating elements 42 and through the drying zonealong generally horizontal paths by a plurality of turbofans 50 (seeFIGS. 3 and 6) that are rotatably mounted centrally of the housing. Thedrying medium is thereafter exhausted from the dryer through a duct 52leading from the upper end of the housing. It is possible, of course, torecirculate the drying medium, or to pass it through a preheater beforefeeding it to the housing 20 to augment the heating capacity of theelements 42. Similarly, where a solvent is used to treat the material-fed to the dryer, the drying medium, which in this instance may be aninert gas, upon being exhausted from the dryer may be fed through asolvent recovery system. Also, further economies can be realized bypassing the effluents from either or both of the exhaust ducts 46 and 52through appropriate heat recovery systems.

The wet material to be processed in the dryer is fed through an inletchute assembly 54 (see FIG. 3A) extending through the upper wallassembly 30 of the housing and is directed, as indicated by the arrows,

onto the uppermost tray 56a of a vertical stack of superimposed trays.Each of the trays 56 is generally annular in plan and is supported forrotation within the housing in a generally horizontal plane by a cageassembly 58.

Turning briefly to FIGS. 3A, 3B and 6, the cage assembly 58 is formed bya multiplicity of circumferentially spaced stanchions 60 that aresecured at either end to suitable frame structures 62 and 64. The upperframe 62 connects with a hollow, rotatable shaft 66, while the bottomframe 64 is bolted to the rotatable upper part 63 of a thrust bearingassembly 65. The cage assembly 58, and hence the trays 56, is caused torotate within the housing by a drive train including a driven gear 68carried by the upper bearing part 63, a driver gear 70, a worm reducer72 and a primer mover 74. A second shaft 67, passing concentricallythrough the thrust bearing assembly 65 and shaft 66, rotates theturbofans 50 within the housing. To this end, the shaft 67 is drivablyconnected to a prime mover 76 (see FIG. 1) through a drive trainincluding a drivebelt 78 and a worm reducer 80 connected directly to theend of the shaft 67. Individual control of the rate of rotation of theturbofans 50 and the trays 56 is therefore possible.

The shafts 66 and 67 are suitably journaled at their upper ends in abearing support 84, while the shaft 67 at its lower end extends throughthe thrust bearing assembly 65. High temperature bearings can beconveniently used for this purpose, although the insulation structureand cooling air flow feature ofthe dryer obviates the need for elaboratecooling system for the bearings.

As the trays 56 revolve, the material carried by each tray istransferred to the next lowest tray. In this fashion the material isprogressively advanced through the dryer to a material dischargeassembly 86 in the bottom of the dryer housing 20, through which it isdischarged, as indicated by the arrows in FIG. 3B, to a carryoffconveyor or the like (not shown). The manner in which the material ispassed from tray to tray within the dryer will be readily understood byreferring to FIG. 11, where an expanded, planar representation of thevertical stack of trays 56 is depicted.

After the material is delivered through the inlet assembly 54, to fallon the upper tray 56a as it rotates beneath the assembly 54, it remainson the tray 5611 for approximately one revolution of the tray. The trayis illustrated in FIG. 11 as rotating in the counterclockwisedirection..It is then wiped over the outer edge of the tray, as will bemore fully described hereinafter, and into a material transfer chute 88awhich extends between the tray 56a and the subjacent tray 56b. As shownby the arrows in FIG. 11, the material is guided by the chute 88a ontothe next lowest tray 56b, where it remains for approximately onerevolution of the tray 56b before being wiped, as before, over the edgeof the tray and into the next lowest transfer chute 88b to be deliveredto the lower tray 560. This process is repeated until the material hasbeen discharged from the dryer through the discharge assembly 86.

That is to say, the material remains on each tray for approximately onerevolution of the tray and is then diverted into the upper end of theassociated transfer chute 88 to be directed onto the next lowest tray.In order that this process of successively passing the material fromtray to tray upon each revolution of the trays can be carried out, it isimportant that material transfer chute 88 for receiving material carriedby a tray be po- I sitioned properly in relation to the position of thetrans fer chute 88 delivering the material to that particular tray. Forexample, in FIG. 11, the material transfer chute 88a must be located ina direction clockwise from the lower end of the material inlet means 54,since, as noted, the trays rotate in the counterclockwise direction, sothat the material will be carried by the tray 56a for approximately afull revolution before reaching the position of the chute 88a.Similarly, the transfer chutes 88b to 88g must be positioned clockwiseof the correspondingly higher transfer chutes 88a to 88f. With thetransfer chutes 88 thus arranged, the material will be delivered to thetrays 56b to 56h at the correct circumferential position to be retainedon the respective trays for nearly a full revolution of the trays. Ofcourse, the length of time the material remains on any one tray can becontrolled by regulating the speed of rotation of the trays.

It is an important feature of the invention that the material isdelivered to the upper tray 56a and is thereafter transferred-betweentrays along a path that is inclined at least over a portion of itslength, thereby minimizing billowing of the material and hence retardingthe formation of dust within the dryer. In FIGS. 3A, 4

and 5, the structure of the material inlet assembly 54 by which thematerial is admitted through the upper wall assembly 30 and delivered tothe upper tray 56a includes an insert member 90 that is received withinan opening provided in the upper wall assembly 30 and rests on aperipheral flange 92 extending around the upper end of the opening. Aplurality of clips 94 are attached to the lower side of the wallassembly 30 and are adapted to receive in sliding relation the flangedupper ends of an inclined chute 96, which is of a width approximatelythe lateral width of the annular tray 56a. Material passing through theinsert 90 is deflected along an inclined path by the side wall 98 (seeFIG. 4) of the chute 96 and is delivered in a gentle manner onto thesurface of the tray 56a as it rotates beneath the lower end of thechute. Feeding of the material to the dryer thus results in minimumbreakage, minimum formation of fines and minimum adhesion of thematerial to the inlet assembly. The laterally outer wall of the chute 96is extended in the direction of rotation of the tray 56a to form abaffle-Iike member 100 for preventing the material from flowing over theouter edge of the tray.

Similarly, the-material transfer chutes 88 are constructed to transferthe material between trays along an inclined path, thereby furtherretarding dust creation and minimizing breakage of the material andadhesion of the material to the transfer chutes. For example, in FIGS.33 and 7, the transfer chute 88g extending between the upper tray 56gand the lower tray 56h, includes an inclined central portion 102g ontowhich the material falls, as indicated by the arrows in FIG. 38,

upon being wiped off the surface of the tray 56g.

Another important feature of the transfer chute construction, is thatthe inclined portion'l02g does not extend to the surface of the tray56h, but terminates well above the tray surface at the upper end of avertically extending portion 104g of the chute that defines an outerboundary for the material and confines it to the surface of the tray56h.

The foregoing configuration of the transfer chutes 88 is preferredinasmuch as it has been discovered that if the inclined portions 102extend over the full distance between adjacent trays the openingsbetween the outer edge of the trays and the adjacent surfaces of thetransfer chutes tend to clog. Attempts to avoid such clogging by spacingthe upper ends of the inclined portions 102 farther from the outer edgesof the trays have proved unsatisfactory since this requires that theheating zone within the housing be undesirably enlarged. On the otherhand, if the portions 102 are more steeply inclined, poor distributionof the material on the lower tray surface results.

' In a preferred embodiment of the transfer chutes, again using thechute 88g as an example, an upper vertical portion 106g and side walls108g are provided on the chute 88 more fully to confine the material asit moves between trays. Each of the transfer chutes 88 is supportedwithin the housing 20 by metal straps 110 and 112 (see FIG. 6) that arebolted, for example, to the side walls 108g of the transfer chute 88g.The straps 110 and 112 are in turn bolted to vertically extending plates114 secured to the support columns 22.

Turning now to the manner in which the material is diverted from thetray surfaces and into the upper ends of the transfer chutes 88, FIG. 6illustrates a pair of wiper arms 116g and 118g extending in close,spaced relation to the surface of the tray 563 for guiding the materialoff the tray and into the transfer chute 88g. It will be understood, ofcourse, that a similar pair of wiper arms 116 and 118 are associatedwith each tray 56 in the dryer.

Preferably, the wiper arm 116g is supported by a strap 120 (see FIG. 6),also bolted to a vertical plate 114, so as to extend from a point nearthe far end, relative to the direction of rotation of the trays, of thetransfer chute 88g and across the surface of the tray 56g in a planegenerally tangential to the inner circumference of the tray to terminateat a point approximately on the inner edge of the tray. The wiper arm118g, on the other hand, is mounted so that its leading end isapproximately equidistant between the inner and outer edges of the tray56g and to extend approximately parallel to the arm 116g. A generallyL-shaped divider member 122g is positioned between the trays 56g and56h, for a purpose hereinafter described, and has bolted to the upperend of its vertical leg 124g the rearward end of the wiper arm 118g. Thehorizontal leg 126g is disposed at approximately a right angle to thevertical leg 124g and extends between the trays 56g and 56h toapproximately the midpoint of the trays (see FIG. 6). The vertical andhorizontal legs of the L- shaped member 122g are joined by a centerportion 128g which is inclined to conform with the inclined portion 102gof the material transfer chute 88g.

Accordingly, as the tray 56g rotates beneath the wiper arms 116g and118g, the material is pushed by the wiper arms off the outer edge of thetray and is deflected by the inclined chute portion 102g onto the nextlowest tray 56h. However, because the vertical leg 124g and the centralinclined portion 128g of the divider member 122g in effect divide thetransfer chute 88g into two separate material flow channels (see FIG.7), the material diverted to the transfer chute by the wiper arm 116g isdeposited on the tray 56h on one side of the horizontal leg 126g of thedivider member while the material diverted by the wiper arm 118g isretained on the other side of the horizontal leg.

By this wiper arm and divider member arrangement not only is thematerial handled in a very delicate manner, but the position occupied onthe tray by the material is interchanged each time the material istransferred to a lower tray. This is clear from FIG. 6, where the arrowsindicate that the material moved off the tray 56g by the wiper arm 116g,i.e., the material occupying the inner half of the upper tray 56g, isdelivered by the transfer chute 88g and divider member 122g to the outerhalf of the next lowest tray 56h. Conversely, the material occupying theouter half of the upper tray is diverted by the wiper arm 118g, transferchute 88g and divider member 122g to the inner half of the lower tray56h. An important advantage is thus realized inasmuch as thorough mixingof the material is achieved, with the result that new moist surfaces arecontinuously being exposed to the drying atmosphere to enhance productquality and uniformity and to increase drying efficiency.

A baffle 130g is disposed along the outer edge of the tray 56gimmediately in advance of the leading end of the transfer chute 88g toprevent loss of the material over the outer edge of the tray.Appropriate angle iron supports 132g and 134g are provided to hold thebaffle 130g in the proper position. Since the area between the wiper arm118g and the baffle 130g converges as the chute 883 is approached, thebaffle 130g preferably is tapered upwardly in the direction of rotationof the tray to provide a boundary of increased height (see FIG. 7). Ifdesired, a support 136g may be attached between the baffle 130g and thewiper ann 118g to stiffen the leading end of the wiper arm.

Upon being delivered to the lower tray 56h, and being carried to therespective portions of the tray by the divider member 122g, the materialis distributed evenly over the tray surface to a predetermined level byan elongate leveler arm 138g. The leveler arm is bolted (see FIG. 6) tothe far side wall 108g of the transfer chute 88g and extends therefromover the tray surface, first in a vertically lengthened portion 140g(see FIG. 7), that acts as a wiper arm to deflect the materialdischarged from the chute 88g on to the tray 56h, and, then, as avertically shortened portion 142g that actually levels the material. Itwill be apparent, of course, that the clearance between the lower edgeof the piston 142g and the tray 56h can be varied to regulate the depthof material on the tray.

Although the above description of the wiper arms 116g and 118g, transferchute 88g, divider member 122g, leveler arm 138g and the associatedbaffles and support structure has been made in connection with only twotrays 56g and 56h of the dryer, it will be understood that correspondingelements are associated with all other trays in the dryer, except asotherwise noted.

After one revolution of the tray 56h, the last tray in the dryer, thematerial is pushed'over the edge of the tray by the wiper arms (notshown) associated with the tray 56h and falls on to the bottom wall ofthe housing 20, where it is pushed upon continued rotation of the traysby one or more blades 144 (see FIG. 3B) suspended from the tray supportstructure to the discharge outlet assembly 86. The blades 144 preferablyare mounted to permit adjustment of the clearance between the blades andthe bottom of the housing. Any suitable arrangement, such as the boltand elongate slot structure 146 illustrated in FIG. 38, can be used forthis purpose. Desirably, the blades 144 extend substantially beyond theouter edges of the trays 56 so that all of the material falling from thelower tray 5611 will be swept along by the blades and discharged fromthe dryer.

The discharge assembly 86 includes a chute 148 of which the sides sloperelatively steeply toward the exhaust end of the chute to ensure thatadhesion of the material to the discharge assembly is kept to a minimum.At the material receiving end, the chute 148 is of a transverse widthsubstantially coextensive with the bottom wall of the housing;therefore, it readily receives the material delivered to the bottom wallfrom the tray 56h. An appropriate carryoff conveyor (not shown), or thelike, may be positioned beneath the chute 148 to remove the driedproduct for packaging or further processing. Alternatively, a vaporlock, for example, a high temperature rotary vapor lock apparatus, maybe connected between the chute 148 and whatever material handlingapparatus is used to carry the material away from the dryer to reducethe loss of heat, drying medium or solvent, as the case may be, acrossthe discharge assembly 86.

Another important feature of the dryer of the present invention is thatit is constructed to permit continuous uninterrupted operation at highlyelevated temperatures, for example, temperatures in the range of l,l F,without damage being caused to the dryer skeletal or housing structureby thermal expansion or contraction of the components thereof andwithout warping or jamming of the moving elements of the dryer. Part ofthis construction includes fully insulating the dryer housing 20 on theside and end walls to reduce heat losses and to maintain as uniform aspossible the temperature at the center and periphery of the drying zone,thus improving product uniformity and reducing the magnitude of thermalstresses created in the housing and tray structure.

The side panel units 28, therefore, take a sandwichlike configuration incross section, including two spaced metal sheets 150 and 152 and afiller of insulating material (see FIG. 3A and 3B). Preferably, twotypes of insulating material are used, a layer 154 of dense material,such as asbestos board or the like, abutting the outer surface of theinner sheet 152, and a looser layer 156, such as a wire-mesh fiberglassblanket, filling the space between the layer 154 and the outer sheet150. The sheets 150 and 152 are secured together at their upper andlower ends by generally Z- shaped end' members 158 and 160,respectively, which are in turn bolted to flanged support elements 162and 164 carried by the skeletal structure of the dryer. Similarly, thesheets 150 and 152 are attached along the sides by Z-shaped members 163(see FIG. 6), thereby forming a complete, enclosing insulating panelunit. At convenient locations around the periphery of the housing 20,one or more gas-tight sight ports 165 (see FIGS. 1 and 3A) may beprovided in the panels 28 to allow visual inspection of the interior ofthe dryer.

Each panel 28 is attached at its sides to adjacent support columns 22,as is illustrated clearly in FIGS. 6 and 8, which are specially designedin accordance with the invention to maintain an unbroken insulatingshield around the dryer housing 20. Turning briefly then to the columnstructure, each column 22 is formed by a pair of L-shaped beams 166 andan elongate plate 168. The beams 166 are welded or otherwise securedtogether at their heels, and to the opposite ends of the plate 168 atthe outer ends of their adjacent legs, to enclose with the plate 168 agenerally triangular area. Desirably, the legs of the beams 166 attachedto the plate 168 are arranged at an angle-relative to each other suchthat the panel units 28 are received between the facing beams 166 ofadjacent columns 22 at approximately right angles.

Associated with each column 22 is a channel member 170 (see FIG. 6), thelegs of which are aligned with the outer legs of the respective L-shapedbeams 166 so as to face the side members 163 of the panel units 28. Thechannel member 170 also has facing flanges 172 at the outer ends of itslegs, to which are bolted the ends of the members 163 and outer sheetsof the adjacent panel units 28. Accordingly, each panel unit 28 isfirmly attached at either side, through the channel members 170, to theadjoining panel units 28, but not so firmly as to prevent expansion andcontraction of the housing 20. In fact, the configuration of the channelmembers l70,by which the panel units 28 are connected to the flanges 172at the outer ends of flexible legs, facilitates lateral inward oroutward movement of the housing walls by allowing limited movement ofthe panels along the circumference of the housing.

To avoid large temperature drops across the housing walls at thelocation of the columns 22 and to preserve the integrity of theinsulation shield, insulation members 174, preferably of asbestosmaterial, are placed within the channel members and are held in positiontherein by elongate metal sheets 176. Additional rigidity may be addedto the housing 20, if desired, by tieing adjacent panel units 28together with metal straps 178 and 180 (see FIGS. 3A and 3B) located atthe upper and lower ends, respectively, of the panels.

The insulation provided in the lower wall assembly 32, as illustrated inFIGS. 33, may consist substantially of asbestos material 182. Thismaterial is contained within a sheet metal enclosure formed by annular,generally L-shaped members 184 underlying the area between the cage 58and the side walls of the housing and a plurality of end sections 186,corresponding in number to the number of panel units 28, that arebolted, as at 188, to the outer end of the L-shaped members 184. The endsections 186 are supported (see FIG. 8) by the channel members 170 insubstantially the same way as the panel units 28, and are furtherconnected at their inner walls 189 to an L-shaped, annular girth member190 carried by the columns 22 in encircling relation of the lower end ofthe dryer.

That portion of the lower end of the dryer located within the cage 58 isinsulated by an annular pad 192 (see FIG. 3B) of asbestos materialenclosed within a sheet metal enclosure 194 and mounted onthe cageassembly frame structure 64 for rotation therewith. The pad 192 overlapsthe inner end of the insulating material 182 to provide a continuity ofinsulation material across the lower end of the dryer. Apertures areformed in the pad 192 and enclosure 194 for passage of the stanchions 60of the cage assembly 58.

The upper wall assembly 30 (see FIG. SA) has the same basic sandwichstructure as the panel units 28, but differs therefrom in that the uppersheet 196 of the assembly, referred to herein for purposes ofillustration as the cold roof; is attached, by welding, for example, tothe upper support frame 26 and the lower sheet 198, referred to hereinas the "hot roof, together with the overlying layers 200 and 202 ofasbestos and fiberglass materials, is carried by the cold roof 196 so asto be movable relative thereto. This is accomplished by suspending thehot roof 198 from the cold roof 196 through the use of a plurality ofpairs of mating, U- shaped brackets 204 and 206 attached to the coldroof 196 and hot roof 198, respectively (see FIGS. 2 and 3A). As the hotroof 198 is supported solely by the brackets 204 and 206, it is free toexpand or contract laterally of the housing in response to variations ofthe temperature within the housing. If desired, the hot roof 198 may betied to an upper girth member 208, which may also carry the elements 162for supporting the panels 28.

To prevent wrinkling of the cold roof 196 caused by the leakage of hotair currents along its lower surface, a gasket 207 (see FIGS. 2 and 3A)is lapped over the end of the hot roof and is held tightly against afacing flange 209 on the cold roof by an L-shaped clamp 211 bolted tothe cold roof. As is apparent from FIG. 2, the gasket 207 and clamp 209extend along the entire periphery of the hot roof.

The upper wall assembly 30 is dimensioned to overlap the upper ends ofthe panel units 28 (see FIG. 3A), thus fully sealing off the drying zonefrom the environment. Moreover, as the cold roof 196 and the uppersupport frame 26 are shielded from the high temperatures within thedryer housing, it possible to position accurately the shafts 66 and 67,the heating elements 42 and the associated fuel intake and exhaustequipment, in relation to the interior of the dryer housing 20, as wellas in relation to the accessory equipment servicing the dryer, and topreserve the alignment of these elements during operation of the dryer.Also, access to the equipment carried by the frame 26 is possible at alltimes. This is important should it develop that adjustments or repairsneed to be made to the equipment during drying operations.

To ensure that the hot roof 198 is free to expand and contract withoutjamming against the heating elements 42 and the various other equipmentextending through the upper wall assembly 30, the openings provided inthe hot roof are oversized and offset from the corresponding openings inthe cold roof 196 to an extent that the hot roof 198 can expand the fulldistance anticipated at the highest operating temperature of the dryerwithout engaging this equipment. For example, in FIG. 3A, the opening210 formed in the hot roof 198 to admit the material inlet assembly 54is significantly larger in size than the corresponding opening in thecold roof 196, i.e., the opening surrounded by the peripheral flange 92.Likewise, the openings 214 (see FIG. 2) for the heating elements 42 arealso enlarged to allow for expansion of the hot roof.

As mentioned, provision is made for permitting expansion and contractionof the dryer housing and its support structure. In a preferredembodiment, such provision includes load-transmitting expansion joints216 (see FIG. 1) located between the lower and upper ends of the supportcolumns 22 and the lower and upper support frames 24 and 26,respectively. All of the expansion joints are identical; therefore, onlyone will be described, it being understood that the description willapply to all equally.

In FIG. 3A, a typical expansion joint 216 includes a pair of spacedplates 218 and 220 to which are attached, respectively, a sleeve 222 anda pair of spaced upstanding ears 224, the sleeve 222 being receivedbetween the ears 224 and in turn receiving, in sliding engagement, a pin226 carried between the ears 224. A set screw 228 may be provided toanchor the pin 226 in fixed position relative to the ears 224.Desirably, the expansion joints 216 are interposed between and bolted tocooperating plates 230 and 232 secured to the ends of the columns 22 andthe support frames 24 and 26 (see FIGS. 3A and 3B), although theselatter plates may be omitted if desired.

Preferably the sleeve 222 and pin 226 of each joint 216 are arranged inalignment with a radius of the housing to facilitate lateral movement ofthe columns 22 as the various dryer elements connected to the columnsexpand or contract during operation of the dryer. Accordingly, each ofthe expansion joints 216 associated with any one column 22 are givenorientations such that both are aligned along the same radius of thehousing (see FIG. 1).

Provision is also made for expansion and contraction of the trays 56 andthe bottom wall of the housing to permit high temperature operation ofthe dryer and to make possible the maintenance of highly elevatedtemperatures in the upper portions of the dryer while using the lowertrays for cooling of the material before discharge. Turning first to thetray structure and referring to FIGS. 38 and 6, where the trays 56g and56h and the support structure therefore are representative of a preferred embodiment, the annular trays 56g and 56h are formed of aplurality of truncated segements 234 supported in a generally horizontalplane in end to end relation on a pair of laterally spaced, L-shapedannular rings 236 and 238. At each vertical position along thestanchions 60 at which a tray 56 is to be located, L- shaped arms 240are mounted thereon to extend radially from the stanchions 60 and to beattached at their outer ends to the vertically depending leg of theouter ring 238. To allow for movement of the ring 238, this attachmenttakes the form of a slidable joint constituted by L-shaped brackets 241(see FIGS. 3B and 6) that are secured to the arms 240 by a bolt andelongate slot arrangement 243.

The inner annular ring 236 is also supported by the radial arms 240, butinstead of being secured directly to the arms, as is the outer ring 238,gaps 242 are formed in the ring (see FIG. 7) so that the ring 236 is infact a plurality of separate arcuate segments. 244 that arecircumferentially spaced at their ends a distance sufficient to allowthe arms 240 to pass between adjacent segments. An annular metal band246 is attached to the upper portion of the vertically extending legs ofthe segments 244 and is notched at 248 (see FIG. 7) at radial positionscorresponding to the positions of the arms 240 so that the band 246 fitsover the arms 240 and rests against the upper horizontal leg of the armsin a manner such that the horizontal upper legs of the segments 244 arein approximately the same plane as the horizontal upper legs of the arms240 and the horizontal upper leg of the outer ring 238. The ring 236 ispositioned relative to the arms 240 and to the axis of rotation of thetrays by stops 245 (see FIG. 3B) welded to the inner end of the arms.

The inner ring 236, therefore, is free to move or float radially alongthe arms 240 in response to thermally induced forces, thus avoidingwarping of the trays due to temperature gradients within the dryer.Also, the band 246 serves to keep the material carried by the trays fromfalling over the inner edges of the trays. Each tray segment 234 ismounted on the inner ring 236 and the outer ring 238 of the tray supportstructure in a manner to permit both circumferential and radialexpansion and contraction of the segments. Thus in FIGS. 3B, 6 and 7,the tray segments 234 are welded, or otherwise secured, at one end tothe horizontal leg of an L-shaped bracket 250, the vertical leg of whichis bolted to the vertical leg of the arm 240. Elongate slots 252 in thebracket 250 allow relative movementbetween the bracket 250 and thesupporting arm 240 due to different rates of expansion or contraction ofthe bracket, or tray segments 234, and the arms 240.

At the other end, and along the inner and outer edges, the tray segments234 are slidably clamped to the horizontal legs of the adjacent arms 240and to the inner ring segments 244 and the outer ring 238, respectively.In FIG. 6, the arrangement of the clamps 254 and the annular rings 236and 238 and arms 240 by which thermal expansion and contraction of thetray segments 234 is possible is clearly shown. There, the clamps 254that coact with the horizontal legs of the inner ring segments 244 andthe outer ring 238 are spaced along the respective edges of the traysegments 234 and are disposed to open in the radially inward directionso as to slip over the outwardly oriented (see FIG. 7) horizontal legsof the rings. Also, the clamps 254 coacting with the horizontal legs ofthe arms 240 are located to open toward the end of the segments 234 andto slip over the facing legs of the arms 240. The individual traysegments 234 are therefore easily installed on or removed from the traysupport structure simply by sliding them inwardly and circumferentiallyto engage the clamps 254 with the respective horizontal legs of theinner and outer rings 236 and 238 and the radial arms 240. Thereafter,the bolts securing the bracket 250 to the vertical leg of the adjacentarm 240 are tightened sufficiently to hold the tray segment in place,but not so tightly as to prevent expansion or contraction of the segmentrelative to the arm.

The bottom wall of the dryer is similarly constructed to allow forthermally induced changes in dimension and is further designed tofacilitate fabrication of the dryer. ln FIGS. 8, 9 and 10, the bottomwall of the dryer is formed by multiple arcuate segments 256 supportedat the outer edges by the annular girth member 190 and at the inneredges by an annular ring 258. Radial arms 260 extend between the innerring 258 and the girth member 190 and support the circumferential endsof the segments 256.

The inner ring 258 is attached to a disc 261 which in turn is attachedto a support plate 262 (see FIG. 3B) attached to the dryer skeletalstructure. Preferably, the ring 258 is arranged so that its vertical legextends upwardly to form a boundary against leakage of the material offthe inner edge of the bottom wall. A similar function is performed atthe outer edge of the bottom wall by the inner walls 189 of the endsections 186 of the lower wall assembly 32.

Each bottom wall segment 256 is attached at one circumferential end (seeFIG. 10) to the horizontal leg of a bracket 266, the bracket 266 beingbolted to the vertical leg of the adjacent arm 260. At the other end,the segment carries on its undersurface, a plurality of L- shaped clampelements 268 for gripping the arms 260. Similar clamp elements 268 arealso positioned along the radially inner and outer edges of the wallsegments to cooperate with the horizontal legs of the ring 258 and thegirth 190, respectively (see FIG. 9).

The clamp elements 268 include a fixed L-shaped bracket 270 and anassociated movable element 272. The movable elements 272 are adjustablevertically, as by a bolt and elongate slot arrangement 274, so as to beabutted against the horizontal legs of the respective support members.With this arrangement, the lower wall of the dryer is readily assembledin that the segments 256 may be dropped in position on the ring 258 andgirth member 190 and thereafter easily secured to the horizontal legs ofthese members and also to the horizontal leg of the adjacent radial arm260. The bracket 266 may then be bolted to the vertical leg of the arm260 to fix the segment 256 in position. However, since the segments 256are fixedly attached to only one arm 260, they are free to expand orcontract in either the radial or circumferential direction. Accordingly,high drying temperatures can be maintained through the vertical extendof the dryer and across the bottom wall, without causing warping ofbuckling of the bottom wall or without causing misalignment of thedischarge assembly 86.

The tray segments 234 and bottom wall segments 256, as well as otherparts of the dryer in contact with the material being dried, may beconstructed of steel or any special alloy. They may also be of corosionresistant and cost saving materials such as enameled steel, asbestoscement board or glass fiber laminates.

During operation a slight negative pressure is preferably maintainedwithin the dryer housing 20 so that at any point on the housingwhereleakage of the drying medium or airborne particles might beexpected an inwardly flow of air will exist. Also, it is an importantfeature of the invention that an inward, pressurized flow of air ismaintained along the shafts 66 and 67 at the points where they extendthrough the dryer housing.

- Thus, an air line 276 associated with the thrust bearing tween theconcentric shafts 66 and 67. It will be appreciated, therefore, that thebearings for both of the shafts 66 and 67 are cooled by these air flowsand that leakage along either shaft is prevented. Furthermore,

the use of the leakage-preventing air flow to cool the bearings in themanner described precludes the need for elaborate cooling systems forthe bearings or the use of expensive high temperature bearing materials.

It will be apparent from the foregoing, that the continuous rotary dryerof the present invention is especially adapted for a wide variety ofapplications;

whether for drying alone; drying and cooling together; drying withsolvent recovery; drying in a superheated vapor atmosphere, for example,where steam is used as the drying medium; for purifying solids bysublimation; for reacting gases with solid material carried by thetrays; and for cooling alone. Moreover, the dryer finds particularapplication where fragile and normally dusty materialsare to beprocessed and where breakage andv dust levels generated during thehandling of these materials are too minimized.

It will further be apparent to those skilled in the art that the abovedescribed embodiments are intended to be merely exemplary, in that theyare susceptible of modification and variation without departing from thespirit of the invention.

We claim:

1. Rotary material processing apparatus, particulary for processingmaterial at high temperatures, comprising:

a vertically extending housing;

inlet means in an upper region of the housing for admitting material tobe processed;

outlet means in a lower region of the housing for discharging theprocessed material;

a plurality of vertically superimposed trays rotatably mounted in thehousing for progressively carrying the material from the inlet means tothe outlet means;

means for transferring the material between trays in a manner tominimize breakage and billowing of the material and thereby to minimizedust creation, said transferring means including l) chute means, havingan inclined portion sloping generally downward from a first point spacedradially beyond one edge of an upper tray and terminating at a secondpoint spaced above the surface of a lower tray by a distance sufficientto prevent clogging of the inclined portion and radially within butadjacent to the corresponding edge of the lower tray, and (2) a retainermember depending from the inclined portion of the chute means andextending downwardly therefrom to terminate at a point closely adjacentthe surface of the lower tray thereby to prevent the materialtransferred to the lower tray from spilling over said edge thereof;

means for diverting the material carried by the upper tray over the oneedge thereof into the chute means; and

means for distributing the material discharged by the chute means overthe surface of the lower tray.

2. Apparatus according to claim 1 wherein the retainer member isgenerally vertical and is attached to the inclined portion at the lowerend thereof.

3. Apparatus according to claim 1 wherein:

the chute means further comprises a generally vertical portion extendingupward from the upper end of the inclined portion thereby to form anentrance for the material carried by the upper tray; and

the retainer member is generally vertical and extends downward from thelower end of the inclined portion.

4. Apparatus according to claim 1 wherein said one edge of the uppertray is the radially outer edge thereof.

5. Apparatus according to claim 1 wherein:

the means for diverting the material into the chute means includesstationary wiper arm means extending across the upper tray in close,spaced relation to the surface thereof in a direction to guide thematerial into the chute means upon rotation of the tray; and

wherein the means for distributing the material over the surface of thelower tray includes stationary leveler arm means extending across thesurface of the lower tray in a direction to guide the materialdischarged from the chute means away from the lower end thereof and tospread the material evenly over the tray surface upon rotation of thetray.

6. Apparatus according to claim 1 further comprising means forinterchanging the location on the trays of discrete radially inner andradially outer portions of the material upon transfer of the materialfrom the upper to the lower tray.

7. Apparatus according to claim 1 wherein the inlet means in the housingincludes inclined chute means for guiding the material onto an uppertray along an inclined path so as to retard breakage or billowing of thematerial.

8. Apparatus according to claim 6 wherein lower end of the inclinedportion of the chute means extending between adjacent trays ispositioned to discharge the material from the upper tray onto the lowertray at a location spaced in the direction of rotation of the trays fromthe upper end of the inclined portion of the chute means extending fromthe said lower tray to the next lower tray, whereby the material iscarried by each tray for approximately one full revolution of the tray.

9. Apparatus according to claim 1 further comprising:

vertically extending shaft means for rotatably supporting the trayswithin the housing;

means located exteriorly of and spaced from the housing for journallingthe shaft means adjacent the upper and lower ends thereof; and

means associated with the journalling means for producing a flow of airinwardly along the shaft means to cool the shaft means and to preventleakage of the material along the shaft means.

10. Rotary material processing apparatus, particularly for processingmaterial at high temperatures, comprising:

a vertically extending housing;

inlet means in an upper region of the housing for admitting material tobe processed;

outlet means in a lower region of the housing for discharging theprocessed material;

a plurality of vertically superimposed trays rotatably mounted in thehousing for progressively carrying the material from the inlet means tothe outlet means; I

means for transferring the material between trays in a manner tominimize breakage and billowing of the material and thereby to minimizedust creation, said transferring means including (1) chute means, havingan inclined portion sloping generally downward from a first point spacedradially beyond one edge of an upper tray and terminating at a secondpoint spaced above the surface of a lower tray by a distance sufficientto prevent clogging of the inclined portion and radially within butadjacent to the corresponding edge of the lower tray, and (2) retainermeans for preventing the material transferred to the lower tray fromspilling over said edge thereof;

means for dividing the chute means into at least two material flowchannels to guide the material occupying a radially inner location onthe upper tray to a radially outer location on the lower tray and thematerial occupying a radially outer location on the upper tray to aradially inner location on the lower tray;

means for diverting the material carried by the upper tray over the oneedge thereof into the chute means; and

means for distributing the material discharged by the chute means overthe surface of the lower tray. 11. Apparatus according to claim whereinthe dividing means includes a generally vertically extending dividermember located approximately centrally of the circumferential extent ofthe chute means and conforming generally at one edge to the laterallyadjacent surface of the chute means, the divider member having at itslower end a laterally projecting portion extending over the lower trayin close, spaced relation to the surface of the tray to terminate atapproximately the midpoint of the tray.

12. Apparatus according to claim 11 wherein: the means for diverting thematerial into the chute means includes stationary wiper arm meansextending across the upper tray in close, spaced relation to the surfacethereof in a direction to guide the material into the chute means uponrotation of the tray; the means for distributing the material over thesurface of the lower tray includes stationary leveler arm meansextending across the surface of the lower tray in a direction to guidethe material discharged from the chute means away from the lower endthereof and to spread the material evenly over the tray surface uponrotation of the tray; and the wiper arm means extending across the uppertray includes (1) a first wiper arm extending from the far end, relativeto the direction of rotation of the tray, of the chute means to a pointapproximately over the radial edge of the tray opposite said one edgeand (2) a second wiper arm extending from the upper end of the dividingmember to a point approximately over the midpoint of the tray, wherebyapproximately half of the material carried by the tray is guided by thefirst wiper arm into the chute means on one side of the dividing memberand approximately half of the material is guided by the second wiper arminto the chute means on the other side of the dividing member.

l3. Rotary material processing apparatus, particularly for processingmaterial at high temperatures, comprising:

a vertically extending housing;

inlet means in an upper region of the housing for admitting material tobe processed;

outlet means in a lower region of the housing for discharging theprocessed material;

a plurality of vertically superimposed trays rotatably mounted in thehousing for progressively carrying the material from the inlet means tothe outlet means, the inlet means including (1 inclined chute means forguiding the material onto an upper tray along an inclined path so as toretard breakage or billowing of the material and (2) a baffle extendingadjacent the radially outer edge of the upper tray and in the directionof rotation of the tray to prevent the material discharged onto the trayfrom spilling over the outer edge of the tray;

means for transferring the material between trays in a manner tominimize breakage and billowing of the material and thereby to minimizedust creation, said transferring means including (1) chute means, havingan inclined portion sloping generally downward from a first point spacedradially beyond the outer edge of an upper tray and terminating at asecond point spaced above the surface of a lower tray by a distancesufficient to prevent clogging of the inclined portion and radiallywithin but adjacent to the outer edge of the lower tray, and 2) retainermeans for preventing the material transferred to the lower tray fromspilling over the outer edge thereof;

means for diverting the material carried by the upper tray over theouter edge thereof into the chute means; and

means for distributing the material discharged by the chute means overthe surface of the lower tray.

1. Rotary material processing apparatus, particulary for processingmaterial at high temperatures, comprising: a vertically extendinghousing; inlet means in an upper region of the housing for admittingmaterial to be proceSsed; outlet means in a lower region of the housingfor discharging the processed material; a plurality of verticallysuperimposed trays rotatably mounted in the housing for progressivelycarrying the material from the inlet means to the outlet means; meansfor transferring the material between trays in a manner to minimizebreakage and billowing of the material and thereby to minimize dustcreation, said transferring means including (1) chute means, having aninclined portion sloping generally downward from a first point spacedradially beyond one edge of an upper tray and terminating at a secondpoint spaced above the surface of a lower tray by a distance sufficientto prevent clogging of the inclined portion and radially within butadjacent to the corresponding edge of the lower tray, and (2) a retainermember depending from the inclined portion of the chute means andextending downwardly therefrom to terminate at a point closely adjacentthe surface of the lower tray thereby to prevent the materialtransferred to the lower tray from spilling over said edge thereof;means for diverting the material carried by the upper tray over the oneedge thereof into the chute means; and means for distributing thematerial discharged by the chute means over the surface of the lowertray.
 2. Apparatus according to claim 1 wherein the retainer member isgenerally vertical and is attached to the inclined portion at the lowerend thereof.
 3. Apparatus according to claim 1 wherein: the chute meansfurther comprises a generally vertical portion extending upward from theupper end of the inclined portion thereby to form an entrance for thematerial carried by the upper tray; and the retainer member is generallyvertical and extends downward from the lower end of the inclinedportion.
 4. Apparatus according to claim 1 wherein said one edge of theupper tray is the radially outer edge thereof.
 5. Apparatus according toclaim 1 wherein: the means for diverting the material into the chutemeans includes stationary wiper arm means extending across the uppertray in close, spaced relation to the surface thereof in a direction toguide the material into the chute means upon rotation of the tray; andwherein the means for distributing the material over the surface of thelower tray includes stationary leveler arm means extending across thesurface of the lower tray in a direction to guide the materialdischarged from the chute means away from the lower end thereof and tospread the material evenly over the tray surface upon rotation of thetray.
 6. Apparatus according to claim 1 further comprising means forinterchanging the location on the trays of discrete radially inner andradially outer portions of the material upon transfer of the materialfrom the upper to the lower tray.
 7. Apparatus according to claim 1wherein the inlet means in the housing includes inclined chute means forguiding the material onto an upper tray along an inclined path so as toretard breakage or billowing of the material.
 8. Apparatus according toclaim 6 wherein lower end of the inclined portion of the chute meansextending between adjacent trays is positioned to discharge the materialfrom the upper tray onto the lower tray at a location spaced in thedirection of rotation of the trays from the upper end of the inclinedportion of the chute means extending from the said lower tray to thenext lower tray, whereby the material is carried by each tray forapproximately one full revolution of the tray.
 9. Apparatus according toclaim 1 further comprising: vertically extending shaft means forrotatably supporting the trays within the housing; means locatedexteriorly of and spaced from the housing for journalling the shaftmeans adjacent the upper and lower ends thereof; and means associatedwith the journalling means for producing a flow of air inwardly alongthe shaft means to cool the shaft means and to prevent leakage of thematerial along the shaft means.
 10. Rotary material processingapparatus, particularly for processing material at high temperatures,comprising: a vertically extending housing; inlet means in an upperregion of the housing for admitting material to be processed; outletmeans in a lower region of the housing for discharging the processedmaterial; a plurality of vertically superimposed trays rotatably mountedin the housing for progressively carrying the material from the inletmeans to the outlet means; means for transferring the material betweentrays in a manner to minimize breakage and billowing of the material andthereby to minimize dust creation, said transferring means including (1)chute means, having an inclined portion sloping generally downward froma first point spaced radially beyond one edge of an upper tray andterminating at a second point spaced above the surface of a lower trayby a distance sufficient to prevent clogging of the inclined portion andradially within but adjacent to the corresponding edge of the lowertray, and (2) retainer means for preventing the material transferred tothe lower tray from spilling over said edge thereof; means for dividingthe chute means into at least two material flow channels to guide thematerial occupying a radially inner location on the upper tray to aradially outer location on the lower tray and the material occupying aradially outer location on the upper tray to a radially inner locationon the lower tray; means for diverting the material carried by the uppertray over the one edge thereof into the chute means; and means fordistributing the material discharged by the chute means over the surfaceof the lower tray.
 11. Apparatus according to claim 10 wherein thedividing means includes a generally vertically extending divider memberlocated approximately centrally of the circumferential extent of thechute means and conforming generally at one edge to the laterallyadjacent surface of the chute means, the divider member having at itslower end a laterally projecting portion extending over the lower trayin close, spaced relation to the surface of the tray to terminate atapproximately the midpoint of the tray.
 12. Apparatus according to claim11 wherein: the means for diverting the material into the chute meansincludes stationary wiper arm means extending across the upper tray inclose, spaced relation to the surface thereof in a direction to guidethe material into the chute means upon rotation of the tray; the meansfor distributing the material over the surface of the lower trayincludes stationary leveler arm means extending across the surface ofthe lower tray in a direction to guide the material discharged from thechute means away from the lower end thereof and to spread the materialevenly over the tray surface upon rotation of the tray; and the wiperarm means extending across the upper tray includes (1) a first wiper armextending from the far end, relative to the direction of rotation of thetray, of the chute means to a point approximately over the radial edgeof the tray opposite said one edge and (2) a second wiper arm extendingfrom the upper end of the dividing member to a point approximately overthe midpoint of the tray, whereby approximately half of the materialcarried by the tray is guided by the first wiper arm into the chutemeans on one side of the dividing member and approximately half of thematerial is guided by the second wiper arm into the chute means on theother side of the dividing member.
 13. Rotary material processingapparatus, particularly for processing material at high temperatures,comprising: a vertically extending housing; inlet means in an upperregion of the housing for admitting material to be processed; outletmeans in a lower region of the housing for discharging the processedmaterial; a plurality of vertically superimposed trays rotatably mountedin the housing foR progressively carrying the material from the inletmeans to the outlet means, the inlet means including (1) inclined chutemeans for guiding the material onto an upper tray along an inclined pathso as to retard breakage or billowing of the material and (2) a baffleextending adjacent the radially outer edge of the upper tray and in thedirection of rotation of the tray to prevent the material dischargedonto the tray from spilling over the outer edge of the tray; means fortransferring the material between trays in a manner to minimize breakageand billowing of the material and thereby to minimize dust creation,said transferring means including (1) chute means, having an inclinedportion sloping generally downward from a first point spaced radiallybeyond the outer edge of an upper tray and terminating at a second pointspaced above the surface of a lower tray by a distance sufficient toprevent clogging of the inclined portion and radially within butadjacent to the outer edge of the lower tray, and (2) retainer means forpreventing the material transferred to the lower tray from spilling overthe outer edge thereof; means for diverting the material carried by theupper tray over the outer edge thereof into the chute means; and meansfor distributing the material discharged by the chute means over thesurface of the lower tray.